1. Field of the Invention
The invention relates to a folding device for a web-fed rotary printing machine for producing a longitudinal fold in the conveying direction of the printed copies, the longitudinal fold being formed after the cylinder crossfold. The device comprises a folding blade provided parallel to the conveying direction and suspended from two drive cranks rotating at the same speed and being disposed parallel to each other with the axes of the crank pins extending transversely to the conveying direction, and from two additional cranks assigned thereto. The additional cranks impart to the folding blade an up-and-down movement. When in its bottom position, the folding blade thrusts the printed copies between two driven folding rollers. The crank radius r1 of the drive crank corresponds to the crank radius r2 of the additional crank, and the additional crank is co-axially mounted on the crank pin of the drive crank. The additional crank is able to be driven, via gears, at the same speed as the drive crank, however, in opposite direction of rotation thereto, such that the crank pin of the additional crank executes a rectilinear, perpendicular stroke.
2. Background Information
The German Laid Open Patent Application No. DE 30 46 051 C2, which corresponds to U.S. Pat. No. 4,509,939, issued Apr. 9, 1985, entitled "Folding Device for Web-fed Rotary Printing Presses", discloses a device of this type, a folding device using two double cranks driven by a planetary gear having a sun gear with internal toothing such that the folding blade executes a stroke, which is perpendicular in every direction, towards the printed copy. The mechanical efforts required to execute this movement are high.